1. Field of the Invention
This invention relates to a carrier to be used in the preparation of a catalyst for use in the production of ethylene oxide, a catalyst obtained by depositing a silver-containing catalytic component on the carrier and used for the production of ethylene oxide, and a method for the production of ethylene oxide by the use of the catalyst.
2. Description of the Related Art
Concerning the catalyst for use in the production of ethylene oxide by gas phase oxidation of ethylene and the carrier therefor, numerous reports have been heretofore introduced to literature.
JP-A-57-171,435, for example, has a description to the effect that a carrier obtained by adding mullite, colloidal silica, etc. to xcex1-alumina having a deliberately lowered sodium content has a high specific surface area, a uniform pore distribution, and moreover high wear-resistant properties. EP-B-0,207,550 has a description to the effect that a carrier having a small impurity is obtained by mixing an aluminum compound with the salt of a Group IA metal in the Periodic Table of the Elements and calcining the resultant mixture and a catalyst using this carrier excels in stability. JP-A-04-363,139 discloses a carrier containing xcex1-alumina the elements of the fourth, fifth, and sixth periods (such as, for example, titanium, tin, and hafnium) of the IIIaxe2x80x94VIIa and IIIbxe2x80x94Vb groups in the Periodic Table of the Elements and contains a description to the effect that a catalyst using this carrier has high selectivity and a long life. Further, U.S. Pat. No. 5,100,859 discloses a carrier comprising high-purity xcex1-alumina, the oxide of an alkaline earth metal, a silicon oxide, and zirconium oxide and contains a description to the effect that a catalyst using this carrier has high initial selectivity and a long life.
We have also proposed a catalyst obtained by depositing silver and cesium as catalytic components on a carrier having a coating layer of amorphous silica disposed on the surface of xcex1-alumina and used for the production of ethylene oxide (U.S. Pat. No. 5,077,256) and a catalyst obtained by disposing a coating layer of amorphous silica-alumina on the surface of xcex1-alumina and depositing silver and cesium as catalytic components on the resultant carrier and used for the production of ethylene oxide (U.S. Pat. No. 5,395,812).
The catalysts which are disclosed in U.S. Pat No. 5,077,256 and U.S. Pat. No. 5,395,812 are excellent in catalytic performance and are fully satisfactory from the commercial point of view. Ethylene oxide, however, is produced on a large scale. Even such a small addition to selectivity as 1%, therefore, results in a notable saving in ethylene as a raw material. In the light of the prominence of the economic effect of such an improvement in the selectivity, the desirability of developing a catalyst of more improved performance for the production of ethylene oxide has been finding growing recognition.
An object of this invention, therefore, is to provide a carrier to be used in the preparation of a catalyst for the production of ethylene oxide, a catalyst obtained by depositing silver-containing catalytic component on the carrier and used for the production of ethylene oxide, and a method for the production of ethylene oxide by the use of the catalyst.
Another object of this invention is to provide a carrier which permits preparation of a catalyst possessed of excellent catalytic performance in terms of activity, selectivity, and life and used for the production of ethylene oxide, a catalyst obtained by using the carrier just described, endowed with excellent catalytic performance, and used for the production of ethylene oxide, and a method for the production of ethylene oxide by the use of the catalyst just described.
The objects mentioned above are accomplished by the following items (1)-(8).
(1) A carrier for the catalyst to be used in the production of ethylene oxide, obtained by adding an aluminum compound, a silicon compound, and an alkali metal compound to a low-alkali content xcex1-alumina powder having an alkali metal content in the range of 1-70 m.mols/kg of powder and calcining the resultant mixture, the aluminum compound content as reduced to aluminum being in the range of 0-3 mols/kg of carrier, the silicon compound content as reduced to silicon in the range of 0.01-2 mols/kg of carrier, and the alkali metal content as reduced to alkali metal in the range of 0.01-2 mols/kg of carrier respectively in the carrier.
(2) A carrier according to the item (1) mentioned above, wherein the atomic ratio of the alkali metal content in the powder/the alkali metal content in the carrier is in the range of 0.0001-0.8.
(3) A method for the production of a carrier to be used in the production of ethylene oxide, which comprises mixing a low-alkali content xcex1-alumina powder having an alkali metal content in the range of 1-70 m.mols/kg of powder with an aluminum compound, a silicon compound, and an alkali metal compound at ratios such that in the produced carrier, the aluminum compound content as reduced to aluminum is in the range of 0-3 mols/kg of carrier, the silicon compound content as reduced to silicon in the range of 0.01-2 mols/kg of carrier, and the alkali metal compound content as reduced to alkali metal in the range of 0.01-2 mols/kg of carrier, forming the resultant mixture in a prescribed shape, and then calcining the formed mixture.
(4) A method according to the item (3) mentioned above, wherein the atomic ratio of the alkali metal content in the powder/the alkali metal content in the carrier is in the range of 0.0001-0.8.
(5) A catalyst to be used in the production of ethylene oxide, obtained by depositing a silver-containing catalytic component on a carrier set forth in the item (1) or the item (2) mentioned above.
(6) A method for the production of a catalyst to be used for the production of ethylene oxide, which comprises depositing a silver-containing catalytic component on a carrier set forth in the item (1) or the item (2) mentioned above and then calcining the resultant composite.
(7) A method according to the item (6) mentioned above, wherein the calcination is effected in the current of an inert gas at a temperature in the range of 400xc2x0-700xc2x0 C.
(8) A method for the production of ethylene oxide, which comprises subjecting ethylene to catalytic gas phase oxidation with a molecular oxygen-containing gas in the presence of a catalyst set forth in the item (5) mentioned above.
The catalyst to be used in the production of ethylene oxide which is obtained by using the carrier of this invention excels in catalytic properties, particularly in selectivity.